U.S. patent application number 15/551654 was filed with the patent office on 2018-02-08 for domestic refrigeration device with a coolant circuit, and method for operating a domestic refrigeration device with a coolant circuit.
The applicant listed for this patent is BSH HAUSGERAETE GMBH. Invention is credited to Tommy BECKMANN, Moritz KLEIN, Achim PAULDURO, Axel WALTER.
Application Number | 20180038622 15/551654 |
Document ID | / |
Family ID | 55236366 |
Filed Date | 2018-02-08 |
United States Patent
Application |
20180038622 |
Kind Code |
A1 |
PAULDURO; Achim ; et
al. |
February 8, 2018 |
Domestic Refrigeration Device With A Coolant Circuit, And Method
For Operating A Domestic Refrigeration Device With A Coolant
Circuit
Abstract
A domestic refrigeration device and a method for operating a
domestic refrigeration device. The domestic refrigeration device
has a heat-insulated body with a coolable inner container which
delimits a coolable interior provided for storing food. A coolant
circuit is provided for cooling the coolable interior and includes
a compressor and a field-oriented electric drive. The
field-oriented electric drive has a field-oriented controller, a
converter, and a permanently excited synchronous motor which is
connected downstream of the converter and which is part of the
compressor or is provided for driving the compressor.
Inventors: |
PAULDURO; Achim; (Albeck,
DE) ; BECKMANN; Tommy; (Durchhausen, DE) ;
WALTER; Axel; (Berlin, DE) ; KLEIN; Moritz;
(Giengen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BSH HAUSGERAETE GMBH |
Muenchen |
|
DE |
|
|
Family ID: |
55236366 |
Appl. No.: |
15/551654 |
Filed: |
January 27, 2016 |
PCT Filed: |
January 27, 2016 |
PCT NO: |
PCT/EP2016/051632 |
371 Date: |
August 17, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 13/00 20130101;
H02P 21/00 20130101; H02P 27/04 20130101; F25B 49/025 20130101;
F25B 2600/024 20130101; H02P 1/46 20130101; F25B 31/026 20130101;
H02P 21/22 20160201; H02P 21/34 20160201 |
International
Class: |
F25B 49/02 20060101
F25B049/02; H02P 21/34 20060101 H02P021/34; F25B 31/02 20060101
F25B031/02; H02P 27/04 20060101 H02P027/04; F25B 13/00 20060101
F25B013/00; H02P 21/22 20060101 H02P021/22; H02P 1/46 20060101
H02P001/46 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2015 |
DE |
10 2015 203 144.6 |
Claims
1-10. (canceled)
11. A method for operating a domestic refrigeration appliance, the
appliance having: a thermally insulated body with a coolable inner
container delimiting a coolable interior chamber for storing food,
a refrigerant circuit for cooling the coolable interior chamber
with a compressor and a controlled electric drive; wherein the
controlled electric drive has a field-oriented controller, a
converter and a permanently excited three-phase synchronous motor,
which is connected downstream of the converter and which is part of
the compressor or configured to drive the compressor; wherein the
field-oriented controller has a first current control circuit
configured to control a transverse current generating a main torque
of the permanently excited three-phase synchronous motor, a second
current control circuit configured to control a longitudinal
current for the permanently excited three-phase synchronous motor
and a speed control circuit super ordinate to the first and second
current control circuits, the speed control circuit generating a
transverse current target value for the first current control
circuit as a function of a predetermined target speed for the
permanently excited three-phase synchronous motor and an actual
speed of the permanently excited three-phase synchronous motor, and
wherein output signals of the first and second current control
circuits are provided at least indirectly to activate the
converter; the method comprising the following method steps: for
starting up the permanently excited three-phase synchronous motor
from standstill, implementing a target speed for the field-oriented
controller as a function of a cooling requirement for the coolable
interior chamber; and approaching a longitudinal current target
value provided for the second current control circuit or its
magnitude starting from "zero" to a predetermined value within a
first time period according to a predetermined profile, to cause
the permanently excited three-phase synchronous motor to generate
an additional torque to the main torque due to a resulting
longitudinal current, so that an overall torque of the permanently
excited three-phase synchronous motor is greater than the main
torque.
12. The method according to claim 11, wherein the first current
control circuit has a first current controller and the second
current control circuit has a second current controller and an
input signal for the first current controller is a deviation of the
transverse current actual value from the transverse current target
value and an input signal for the second current controller is a
deviation of the longitudinal current actual value from the
longitudinal current target value.
13. The method according to claim 11, which comprises adjusting the
longitudinal current target value or a magnitude thereof in a ramp
shape during the first time period and which comprises storing an
adjustment profile in a look-up table or determining the adjustment
profile by way of a mathematical formula.
14. The method according to claim 11, which comprises adjusting the
longitudinal current target value or a magnitude thereof in
accordance with an adjustment profile stored in a look-up table or
determined by way of a mathematical formula.
15. The method according to claim 11, which further comprises:
reducing the longitudinal current target value or a magnitude
thereof to "zero" as soon as the permanently excited three-phase
synchronous motor reaches a stable working point or after a
predetermined second time period; and subsequently operating the
field-oriented controller with a longitudinal current target value
equal to "zero."
16. The method according to claim 14, which comprises reducing the
longitudinal current target value or the magnitude thereof from a
predetermined value to "zero" within a predetermined third time
period according to a predetermined profile.
17. A domestic refrigeration appliance, comprising: a thermally
insulated body with a coolable inner container delimiting a
coolable interior chamber for storing food; a refrigerant circuit
configured to cool said coolable interior chamber, said refrigerant
circuit including a compressor and a field-oriented electric drive,
which has a field-oriented controller, a converter and a
permanently excited three-phase synchronous motor, which is
connected downstream of said converter and which forms part of said
compressor or is configured to drive said compressor; said
field-oriented controller having a first current control circuit
provided to control a transverse current generating a main torque
of said permanently excited three-phase synchronous motor, a second
current control circuit provided to control a longitudinal current
for said permanently excited three-phase synchronous motor and a
speed control circuit super ordinate of said first and second
current control circuits, said speed control circuit generating a
transverse current target value for said first current control
circuit as a function of a predetermined target speed for said
permanently excited three-phase synchronous motor and an actual
speed of said permanently excited three-phase synchronous motor;
said first and second current control circuits carrying output
signals for directly or indirectly activating said converter, and
wherein: for starting up said permanently excited three-phase
synchronous motor from standstill, a target speed for said
field-oriented controller is determined as a function of a cooling
requirement for said coolable interior chamber, and a longitudinal
current target value for said second current control circuit or a
magnitude thereof is adjusted starting from "zero" to a
predetermined value within a first time period according to a
predetermined profile, to cause said permanently excited
three-phase synchronous motor to generate an additional torque to
the main torque due to the resulting longitudinal current, so that
an overall torque of said permanently excited three-phase
synchronous motor is greater than the main torque.
18. The domestic refrigeration appliance according to claim 17,
wherein said first current control circuit has a first current
controller and said second current control circuit has a second
current controller and an input signal for said first current
controller is a deviation of the transverse current actual value
from the transverse current target value and an input signal for
said second current controller is a deviation of the longitudinal
current actual value from the longitudinal current target
value.
19. The domestic refrigeration appliance according to claim 17,
wherein an adjustment of the longitudinal current target value or
the magnitude thereof is ramp-like during the first time period
and/or wherein a profile of the adjustments is stored in a look-up
table or is calculated by way of a mathematical formula.
20. The domestic refrigeration appliance according to claim 17,
wherein the longitudinal current target value or the magnitude
thereof is decreased to "zero" as soon as said permanently excited
three-phase synchronous motor reaches a stable working point or
after a predetermined second time period, and wherein the
field-oriented controller is subsequently operated with a
longitudinal current target value equal to "zero."
21. The domestic refrigeration appliance according to claim 20,
wherein the longitudinal current target value or the magnitude
thereof is reduced from its predetermined value to "zero" within a
predetermined third time period according to a predetermined
profile.
Description
[0001] The invention relates to a domestic refrigeration appliance
with a refrigerant circuit and a method for operating a domestic
refrigeration appliance with a refrigerant circuit.
[0002] Domestic refrigeration appliances comprise a coolable
interior chamber for storing food and a refrigerant circuit for
cooling the coolable interior chamber. The refrigerant circuit in
particular comprises a compressor, a condenser connected downstream
of the compressor, a restrictor apparatus connected downstream of
the condenser and an evaporator, which is arranged between the
restrictor apparatus and the compressor.
[0003] DE 10 2010 030 240 A1 discloses such a domestic
refrigeration appliance, in which the compressor is driven with a
brushless direct current motor. A brushless direct current motor is
generally a permanently excited three-phase synchronous motor. The
brushless direct current motor is activated by an inverter.
[0004] Permanently excited three-phase synchronous motors can be
part of a controlled electric drive, the controller of which can be
configured as a field-oriented controller known in principle to the
person skilled from DE 102 06 191 B4 for example. With
field-oriented control, also referred to as vector control, the
electric voltages and currents of the three-phase synchronous motor
are combined in the form of space vectors. The space vectors relate
to a fixed-stator coordinates system and move synchronously with
the rotor of the three-phase synchronous motor. In order to relate
the variables to the rotor, said variables are transformed to a
fixed-rotor d, q coordinates system.
[0005] For field-oriented control a control structure results, with
which the transformed currents i.sub.d (longitudinal current),
i.sub.q (transverse current) are controlled, preferably by means of
PI controllers. Such current controllers form internal current
control circuits within a cascade structure, with an external speed
control circuit superimposed thereon. The transverse current
i.sub.q here mainly supplies the torque (main torque) of the
three-phase synchronous motor. The target value of the current
control loop for the longitudinal current i.sub.d is generally
"zero". FIG. 1 of DE 102 06 191 B4 shows such a control structure
for an asynchronous motor. When a three-phase synchronous motor is
used, the flux calculator cited in DE 102 06 191 B4 is omitted and
the target value of the current control loop for the longitudinal
current i.sub.d is "zero".
[0006] With permanently excited three-phase synchronous motors, as
for example with what are referred to as brushless direct current
motors (BLDC motors) the transverse inductances L.sub.q and
longitudinal inductances L.sub.d assigned to the transverse and
longitudinal currents can have different values. The longitudinal
current i.sub.d can therefore also supply a torque (reluctance
contribution, reluctance torque).
[0007] It is also known for example from DE 102 06 191 B4 that with
the permanently excited three-phase synchronous motor the speed
range can be extended upward if a field-counteracting current is
injected in the upper speed range. To this end the target value of
the current control loop for the longitudinal current i.sub.d is
selected as smaller than "zero", thereby however reducing the
overall torque of the permanently excited three-phase synchronous
motor. This is referred to as field weakening mode.
[0008] It is the object of the invention to specify a domestic
refrigeration appliance, which has a coolable interior chamber and
a refrigerant circuit provided to cool the coolable interior
chamber with a compressor, the electric drive of which is provided
to drive the compressor, has a permanently excited three-phase
synchronous motor and has an improved operating response, in
particular an improved start-up response.
[0009] The object of the invention is achieved by a domestic
refrigeration appliance, having a thermally insulated carcass with
a coolable inner container, which delimits a coolable interior
chamber provided to store food, a refrigerant circuit provided to
cool the coolable interior chamber with a compressor and a
controlled electric drive, which has a field-oriented controller, a
converter and a permanently excited three-phase synchronous motor,
which is connected downstream of the converter and which is part of
the compressor or is provided to drive the compressor, the
field-oriented controller having a first current control circuit
provided to control a transverse current generating a main torque
of the permanently excited three-phase synchronous motor, a second
current control circuit provided to control a longitudinal current
for the permanently excited three-phase synchronous motor and a
speed control circuit superimposed on the current control circuits,
which generates a transverse current target value for the first
current control circuit as a function of a predetermined target
speed for the permanently excited three-phase synchronous motor and
an actual speed of the permanently excited three-phase synchronous
motor, and the output signals of the two current control circuits
are provided at least indirectly to activate the converter, and the
domestic refrigeration appliance being designed to determine a
target speed for the field-oriented controller as a function of a
cooling requirement for the coolable interior chamber to start up
the permanently excited three-phase synchronous motor from
stationary and to adjust a longitudinal current target value
provided for the second current control circuit or its magnitude
starting from "zero" to a predetermined value within a first time
period according to a predetermined profile, so that the
permanently excited three-phase synchronous motor generates an
additional torque to the main torque due to the resulting
longitudinal current, so that the overall torque of the permanently
excited three-phase synchronous motor is greater than the main
torque.
[0010] A further aspect of the invention is a method for operating
a domestic refrigeration appliance, which has a thermally insulated
carcass with a coolable inner container, which delimits a coolable
interior chamber provided to store food, a refrigerant circuit
provided to cool the coolable interior chamber with a compressor
and a field-oriented electric drive, the field-oriented controlled
electric drive having a field-oriented controller, a converter and
a permanently excited three-phase synchronous motor, which is
connected downstream of the converter and which is part of the
compressor or is provided to drive the compressor, the
field-oriented controller having a first current control circuit
provided to control a transverse current generating a main torque
of the permanently excited three-phase synchronous motor, a second
current control circuit provided to control a longitudinal current
for the permanently excited three-phase synchronous motor and a
speed control circuit superimposed on the current control circuits,
which generates a transverse current target value for the first
current control circuit as a function of a predetermined target
speed for the permanently excited three-phase synchronous motor and
an actual speed of the permanently excited three-phase synchronous
motor, and the output signals of the two current control circuits
are provided at least indirectly to activate the converter, having
the following method steps: [0011] for starting up the permanently
excited three-phase synchronous motor from stationary, implementing
a target speed for the field-oriented controller as a function of a
cooling requirement for the coolable interior chamber, and [0012]
approaching a longitudinal current target value provided for the
second current control circuit or its magnitude starting from
"zero" to a predetermined value within a first time period
according to a predetermined profile, so that the permanently
excited three-phase synchronous motor generates an additional
torque to the main torque due to the resulting longitudinal
current, so that the overall torque of the permanently excited
three-phase synchronous motor is greater than the main torque.
[0013] The inventive domestic refrigeration appliance is thus
configured to execute the inventive method.
[0014] The inventive domestic refrigeration appliance comprises the
thermally insulated carcass with the inner container, which
delimits the coolable interior chamber. The coolable interior
chamber is provided to store food and is cooled by means of the
refrigerant circuit.
[0015] The coolable interior chamber can preferably be closed by
means of a door leaf. The door leaf is preferably mounted in such a
manner that it can pivot in relation to an axis which preferably
runs vertically. The coolable interior chamber is accessible in the
opened state.
[0016] The refrigerant circuit per se is known in principle to the
person skilled in the art and comprises the compressor and in
particular a condenser connected downstream of the compressor, a
restrictor apparatus connected downstream of the condenser and an
evaporator, which is arranged between the restrictor apparatus and
the compressor.
[0017] During operation of the inventive domestic refrigeration
appliance the compressor is driven by means of the permanently
excited three-phase synchronous motor. The permanently excited
three-phase synchronous motor can also be part of the
compressor.
[0018] During operation of the compressor the permanently excited
three-phase synchronous motor is operated at a speed determined or
predetermined for example by an electronic control apparatus or a
temperature controller. The permanently excited three-phase
synchronous motor is therefore part of the controlled electric
drive. The electric controlled drive is based on field-oriented
control for an improved control response.
[0019] The field-oriented controller comprises the two current
control circuits, of which the first current control circuit is
provided to control the transverse current and the second current
control circuit is provided to control the longitudinal current of
the permanently excited three-phase synchronous motor. The output
signals of the two current control circuits are provided to
activate the converter at least indirectly. The reference variable
of the first current control circuit is in particular the
transverse current target value and the reference variable of the
second current control circuit is in particular the longitudinal
current target value.
[0020] The first current control circuit can preferably have a
first current controller and the second current control circuit can
preferably have a second current controller. The two current
controllers are preferably PI current controllers. The input signal
for the first current controller is preferably a deviation of the
transverse current actual value from the transverse current target
value and the input signal for the second current controller is
preferably a deviation of the longitudinal current actual value
from the longitudinal current target value.
[0021] Superimposed on the two current control circuits is the
speed control circuit, which generates the transverse current
target value for the first current control circuit as a function of
a predetermined target speed for the permanently excited
three-phase synchronous motor and an actual speed of the
permanently excited three-phase synchronous motor. The reference
variable of the speed control circuit is preferably the target
speed of the permanently excited three-phase synchronous motor.
[0022] The speed control circuit preferably comprises a speed
controller, which is embodied in particular as a PI speed
controller. The input signal for the speed controller is preferably
a deviation of the actual speed from the target speed.
[0023] As already set out in the introduction, the transverse
current is responsible for the main torque of the permanently
excited three-phase synchronous motor. With permanently excited
three-phase synchronous motors however the longitudinal current can
also generate an additional torque, which increases the overall
torque of the permanently excited three-phase synchronous motor
when applied correspondingly. This is the case in particular with
brushless direct current motors, which is why the permanently
excited three-phase synchronous motor is preferably a brushless
direct current motor.
[0024] In order to improve the start-up response of the compressor
or permanently excited three-phase synchronous motor, according to
the invention a target torque is first determined with the
permanently excited three-phase synchronous motor stationary for
example by means of the electronic control apparatus based on a
required cooling of the coolable interior chamber, in order to
operate the field-oriented controller or the speed control circuit
or the speed controller accordingly. This produces the main
torque.
[0025] In order to obtain additional torque to the main torque
during start-up, according to the invention the longitudinal
current target value is predetermined accordingly. According to the
invention the longitudinal current target value provided for the
second current control circuit or its magnitude is adjusted or
increased starting from "zero" to the predetermined value in such a
manner within the first time period that the overall torque of the
permanently excited three-phase synchronous motor is greater than
the main torque. Because the longitudinal current target value or
its magnitude is also approached, preferably constantly increased,
within the first time period according to a predetermined profile,
there is no need for complex calculation of the longitudinal
current target value, with the result that the computation power of
the domestic refrigeration appliance can be relatively low.
[0026] The constant increasing of the longitudinal current target
value or its magnitude is preferably ramp-like during the first
time period. The profile of the adjustment, preferably of the
constant increasing, is preferably stored in a look-up table. The
look-up table can be for example part of the electronic control
apparatus. The profile can also be determined by means of a
mathematical formula.
[0027] As soon as the permanently excited three-phase synchronous
motor has been started up, provision can be made for the
longitudinal current target value to be reduced to "zero"
again.
[0028] According to one embodiment provision is therefore made for
reducing the longitudinal current target value or its magnitude to
"zero" as soon as the permanently excited three-phase synchronous
motor reaches a stable working point, in order then to operate the
field-oriented controller with a longitudinal current target value
equal to "zero". The stable working point can be identified for
example when the deviation between the target speed and the actual
speed is below a predetermined value.
[0029] According to one embodiment provision is preferably made for
reducing the longitudinal current target value or its magnitude to
"zero" after a predetermined second time period, in order then to
operate the field-oriented controller with a longitudinal current
target value equal to "zero". As the second time period is
predetermined, relatively little computation power is needed again.
The second time period is in particular selected to be of such a
length that the permanently excited three-phase synchronous motor
reaches a stable working point reliably.
[0030] In order in particular to embody the electric drive
relatively robustly, the longitudinal current target value or its
magnitude is preferably reduced from its predetermined value to
"zero" within a predetermined third time period according to a
predetermined profile. This profile is preferably ramp-like and/or
preferably stored in the look-up table.
[0031] In order also to be able to operate the permanently excited
three-phase synchronous motor at relatively high speeds, provision
can be made for operating the electric drive in a field weakening
mode.
[0032] An exemplary embodiment of the invention is shown by way of
example in the accompanying schematic drawings, in which:
[0033] FIG. 1 shows a perspective view of a domestic refrigeration
appliance,
[0034] FIG. 2 shows a refrigerant circuit of the domestic
refrigeration appliance,
[0035] FIG. 3 shows an electric drive controlled in a
field-oriented manner for the compressor of the refrigerant
circuit, and
[0036] FIG. 4 shows a part of the current controller of the
field-oriented controller.
[0037] FIG. 1 shows a perspective view of a domestic refrigeration
appliance 1, which comprises a thermally insulated carcass 10 with
an inner container 2, which delimits a coolable interior chamber 3.
The coolable interior chamber 3 is provided for storing food (not
shown in detail).
[0038] In the present exemplary embodiment the domestic
refrigeration appliance 1 has a pivotable door leaf 4 for closing
the coolable interior chamber 3. The door leaf 4 is mounted in
particular in such a manner that it can pivot in relation to a
vertical axis. The coolable interior chamber 3 is accessible when
the door leaf 4 is open, as shown in FIG. 1.
[0039] In the present exemplary embodiment a number of door trays 5
for storing food are arranged on the face of the door leaf 4 facing
in the direction of the coolable interior chamber 3. In particular
a number of compartment bases 6 for storing food are arranged in
the coolable interior chamber 3 and in particular a drawer 7, in
which food can also be stored, is arranged in the lower region of
the coolable interior chamber 3.
[0040] The domestic refrigeration appliance 1 comprises a
refrigerant circuit 20, shown in FIG. 2, for cooling the coolable
interior chamber 3. In the present exemplary embodiment the
refrigerant circuit 20 of the coolable interior chamber 3 comprises
a compressor 21, a condenser 22 connected downstream of the
compressor 21, a restrictor apparatus 23 connected downstream of
the condenser 22, which is embodied in particular as a restrictor
tube or capillary tube, and an evaporator 24, which is arranged
between the restrictor apparatus 23 and the compressor 21. The
compressor 21 is preferably arranged within a machine chamber of
the domestic refrigeration appliance 1, which is located in
particular behind the drawer 7.
[0041] In the present exemplary embodiment the domestic
refrigeration appliance 1 comprises an electronic control apparatus
8, which is designed to activate the refrigeration apparatus, in
particular the compressor 21 of the refrigerant circuit 20, in a
manner generally known to the person skilled in the art in such a
manner that the coolable interior chamber 3 has at least roughly a
predetermined or predeterminable target temperature. The electronic
control apparatus 8 is preferably designed such that it controls
the temperature of the coolable interior chamber 3. In order to
obtain the actual temperature of the coolable interior chamber 3 if
required, the domestic refrigeration appliance 1 can have at least
one temperature sensor (not shown in detail) connected to the
electronic control apparatus 8.
[0042] In order to activate or control the refrigerant circuit 20,
the domestic refrigeration appliance comprises a controlled
electric drive 30, as shown in FIG. 3, which has a permanently
excited three-phase synchronous motor, which is preferably embodied
as a brushless direct current motor 31. The brushless direct
current motor 31 is coupled to the compressor 21 or is part of the
compressor 21 and drives this as required according to a target
speed n.sub.tar predetermined by the electronic control apparatus
8. The target speed n.sub.tar is calculated or predetermined in
particular by the electronic control apparatus 8 based on an
intended cooling of the coolable interior chamber 3, for example
based on the current temperature and the target temperature of the
coolable interior chamber 3.
[0043] The controlled electric drive 30 comprises a controlling
element for driving the brushless direct current motor 31. The
controlling element is embodied as a converter 32 and generates a
three-phase or multiphase voltage during operation of the electric
drive 30, the fundamental oscillation of said voltage having a
fundamental frequency and amplitude which are an indirect function
of the target speed n.sub.tar and an actual speed n.sub.act of the
brushless direct current motor 31.
[0044] In the present exemplary embodiment the controlled electric
drive 30 has measurement apparatuses 33, which are used to measure
the electric phase currents i.sub.1,2,3 of the brushless direct
current motor 31 and to determine the actual speed. The measurement
apparatuses 33 edit the determined actual speed n.sub.act and the
measured electric phase currents i.sub.1,2,3 of the brushless
direct current motor 31 as required, so that the determined actual
speed n.sub.act and the measured electric phase currents
i.sub.1,2,3 of the brushless direct current motor 31 can be
processed by a field-oriented controller 34 of the controlled
electric drive 30 in a suitable form. The actual speed n.sub.act
can be determined for example, as provided for in the present
exemplary embodiment, from the measured phase currents i.sub.1,2,3.
The actual speed n.sub.act can however also be measured directly
using an appropriate sensor.
[0045] In the present exemplary embodiment the control of the
controlled electric drive 30 is based on field-oriented control.
The principal control structure of such control is known for
example from DE 102 06 191 B4, as cited in the introduction. The
essential difference between the field-oriented control of the
electric drive 30 and conventional field-oriented control is the
predetermination of the target values for the longitudinal current
i.sub.d during operation of the domestic refrigeration appliance 1,
in particular for starting up the compressor 21 or the brushless
direct current motor 31.
[0046] The field-oriented controller 34 forms a cascade structure
with internal current control circuits, on which an external speed
control circuit is superimposed.
[0047] A control structure in which the transformed transverse and
longitudinal currents i.sub.q, i.sub.d are controlled by means of
the current control circuits results for field-oriented control. In
the present exemplary embodiment the current control circuits
preferably comprise a first current controller 41 for the
transverse current i.sub.q and a second current controller 41 for
the longitudinal current i.sub.d. The two current controllers 41,
42 are in particular PI controllers.
[0048] In the present exemplary embodiment the field-oriented
controller 34 is embodied in such a manner that it transforms the
phase currents i.sub.1,2,3 of the brushless direct current motor 31
into fixed-rotor longitudinal and transverse current actual values
i.sub.s,d, i.sub.s,q relating to the rotor of the brushless direct
current motor 31. The deviation between the target value
i.sub.q,tar of the transverse current i.sub.q and the transverse
current actual value i.sub.s,q is the input signal for the first
current controller 41 and the deviation between the longitudinal
current target value i.sub.d,tar and the longitudinal current
actual value i.sub.s,d is the input signal for the second current
controller 42.
[0049] The output signals of the two current controllers 41, 42
correspond to transformed electric voltages u.sub.q, u.sub.d, which
are transformed by means of a transformation (not shown but known
in principle to the person skilled in the art) into signals
suitable for activating the converter 32.
[0050] In the present exemplary embodiment the transverse current
target value i.sub.q,tar results from this external speed control
circuit, which is calculated as a function of the target speed
n.sub.tar and the actual speed n.sub.act, in particular as a
function of the speed deviation n.sub.dev, which results from the
measured and predetermined target speed n.sub.tar.
[0051] In the present exemplary embodiment the speed control
circuit comprises a speed controller 43, which is preferably
embodied as a PI controller. The output signal of the speed
controller 43 is the transverse current target value
i.sub.q,tar.
[0052] The brushless direct current motor 31 is embodied in such a
manner that the longitudinal current i.sub.d is also able to form a
torque-forming component, which acts in addition to the main torque
generated by the transverse current i.sub.q with a corresponding
longitudinal current i.sub.d. It is thus possible to increase the
overall torque above the main torque of the brushless direct
current motor 31 with a corresponding longitudinal current
i.sub.d.
[0053] In the present exemplary embodiment the domestic
refrigeration appliance 1 is embodied in such a manner that it
generates different longitudinal current target values
i.sub.d,tardepending on the operating mode. The longitudinal
current target values i.sub.d,tar are preferably saved in a look-up
table, which is stored in particular in the electronic control
apparatus 8, or are determined by means of a mathematical
equation.
[0054] The decision as to which longitudinal current target value
i.sub.d,tar is currently applicable is illustrated in FIG. 4 by a
function block 44, which actuates a function switch 45.
[0055] As the compressor 21 starts up, in other words as the
stationary brushless direct current motor 31 starts up to a target
speed n.sub.tar in the present exemplary embodiment the electronic
control apparatus 8 first predetermines the target speed n.sub.tar
for the brushless direct current motor 31. The controlled electric
drive 30 is also first operated in a start-up mode, as illustrated
functionally by function blocks AF1 and AF2 in FIG. 4.
[0056] In start-up mode the longitudinal current target value
i.sub.d,tar or its magnitude is first increased constantly starting
from "zero" according to a predetermined profile, until the
longitudinal current target value i.sub.d,tar or its magnitude
reaches a predetermined value. The longitudinal current target
value i.sub.d,tar here is selected such that as a result the
brushless direct current motor 31 generates an additional torque to
the main torque generated by the transverse current i.sub.q, said
additional torque becoming ever larger due to the constantly
increasing longitudinal current i.sub.d, so that the overall torque
of the brushless direct current motor 31 is greater than the main
torque. The profile of the constant increasing is permanently
predetermined and is preferably stored in the look-up table.
[0057] The longitudinal current target value i.sub.d,taror its
magnitude is preferably increased in a ramp-like manner starting
from "zero", as shown by the function block AF1. For this part of
start-up mode the function block 44 switches the function switch 45
to a switch position "A1".
[0058] In the present exemplary embodiment the increasing of the
longitudinal current target value i.sub.d,tar or its magnitude is
time controlled, in other words the longitudinal current target
value i.sub.d,taror its magnitude reaches its predetermined value
after a predetermined first time period T.sub.1. When said
predetermined value is reached, the vectors of the longitudinal
current i.sub.d and the vector of the transverse current i.sub.q
have a defined angle in the settled or adjusted state.
[0059] In the present exemplary embodiment provision is made for
the longitudinal current target value to be set to "zero" after the
end of start-up mode, in particular when the brushless direct
current motor 31 reaches a stable working point and in particular
is to be operated at a relatively low speed or at a speed below the
maximum speed of preferably less than 0.6 times the maximum speed.
This is illustrated by a function block N in FIG. 4.
[0060] The stable working point is reached for example when the
speed deviation n.sub.dev, which results from the measured actual
speed n.sub.actand the predetermined target speed n.sub.tar, is
below a predetermined value.
[0061] In the present exemplary embodiment provision is however
also made for the longitudinal current target value i.sub.d,tar to
be set to "zero" after a predetermined second time period T.sub.2
after the end of the first time period T.sub.1. When the
longitudinal current target value i.sub.d,tar is set to "zero", the
function switch 45 is switched to a switch position "B".
[0062] In the present exemplary embodiment however the longitudinal
current target value i.sub.d,tar is not set to "zero" abruptly but
is returned constantly from its predetermined value to "zero". This
is preferably carried out within a predetermined third time period
T.sub.3. The longitudinal current target value i.sub.d,taror its
magnitude is preferably reduced in a ramp-like manner starting from
the predetermined value, as shown by ii the function block AF2.
[0063] For this part of start-up mode the function block 44
switches the function switch 45 to a switch position "A2".
[0064] In the present exemplary embodiment provision is also made
for the brushless direct current motor 31 to be able to be operated
at a higher speed. To achieve this, the electric drive 30 can be
operated in a field weakening mode, as shown by a function block FS
in FIG. 4. The field weakening mode of a permanently excited
three-phase synchronous motor is known in principle to the person
skilled in the art and is therefore not described here.
[0065] In field weakening mode a field-counteracting current is
injected into the brushless direct current motor 31. To this end
the longitudinal current target value i.sub.d,tar is selected to be
smaller than "zero". For field weakening mode the function switch
45 is switched to a switch position "D".
LIST OF REFERENCE CHARACTERS
[0066] 1 Domestic refrigeration appliance [0067] 2 Inner container
[0068] 3 Coolable interior chamber [0069] 4 Door leaf [0070] 5 Door
tray [0071] 6 Compartment bases [0072] 7 Drawer [0073] 8 Electronic
control apparatus [0074] 10 Carcass [0075] 20 Refrigerant circuit
[0076] 21 Compressor [0077] 22 Condenser [0078] 23 Restrictor
apparatus [0079] 24 Evaporator [0080] 30 Controlled electric drive
[0081] 31 Brushless direct current motor [0082] 32 Converter [0083]
33 Measurement apparatuses [0084] 34 Field-oriented controller
[0085] 41, 42 Current controller [0086] 43 Speed controller [0087]
44 Function block [0088] 45 Function switch [0089] AF1, AF2
Function block [0090] A1, A2, B, C Switch position [0091] FS, N
Function block [0092] i.sub.s,d Longitudinal current actual value
[0093] i.sub.s,q Transverse current actual value [0094] i.sub.q,tar
Transverse current target value [0095] i.sub.d,tar Longitudinal
current target value [0096] i.sub.1,2,3 Phase currents [0097]
n.sub.tar Target speed [0098] u.sub.q, u.sub.d Transformed electric
voltages [0099] n.sub.dev Speed deviation
* * * * *